Orthopedic implants are used for resurfacing or replacing joints, such as knees, hips, shoulders, ankles, and elbows that typically experience high levels of stress and wear or traumatic injury. Implants used to replace these joints must be strong and able to withstand the daily stress and wear at these joints, especially for weight-bearing knee and hip replacements. But providing a sufficiently strong implant that also fits properly is challenging. Traditional orthopedic implants are made from polymer, ceramic, metal or other appropriate material and formed so that they fit the patient's bone securely. In knee replacement surgeries, for example, typical approaches involve cutting the end of the tibia and/or femur, then fitting a new implant to the cut end. The size of the implant is typically determined by the surgeon based on hand measurements and visual estimates. The size and fit between the bone and implant can vary—in some cases being too loose, and in others too tight.
Computer assisted methods have been developed that provide a graphical image of the resected bone and design software that allow the surgeon to install the implant to fit the surgical site more precisely. During a computer-assisted surgery (CAS), a surgeon registers the patient's anatomical site by touching various landmarks around the patient's joint using a registration tool. Once the registration process is completed, the surgeon uses a surgical tool (e.g., cutter) to resect the bone in the patient's joint. The surgical tool may be guided by a computer assisted system.
There are, however, drawbacks to conventional registration processes. A surgeon typically uses a foot pedal or needs an assistant's help during the registration process. The surgeon is required to hold the registration tool steady against a smooth bone surface. While the surgeon is holding the tool, the surgeon's assistant notifies the computer what registration point the surgeon is registering. Also, to register a single point the surgeon may need to change the orientation of the registration tool in various angles with respect to the registration point to ensure that a tracking camera accurately captures the location. This registration process is tedious, time-consuming, and prone to errors.
Conventional CAS systems also include a reference array, which is made of light-reflective material that can be viewed on video camera and used to track the position of a surgical tool during the surgery. The reference array is positioned on the patient or near the patient, but it can be bumped easily and misaligned if anyone moves the operating table or pushes the reference array. When that happens, the patient's anatomic location needs to be re-registered, which prolongs the surgery time. Unfortunately, the surgeon may find it difficult to re-locate the same anatomical landmark sites registered previously, and therefore it may be difficult to re-register the site, possibly reducing the accuracy of the surgical procedure.
In some cases, a surgeon defines a bone cutting boundary pre-operatively based on the 3D model of a patient's joint or MRI or CT image of the patient. Therefore, the accuracy of the surgical procedure may depend on how well the registered bone (which is based on 3D model or an image of the patient) matches the physical bone. That matching can be difficult to achieve. There is a need for a registration process that allows the surgeon to repeatedly and more efficiently register a patient's bone for surgery.